# HG changeset patch
# User mdoerr
# Date 1460025238 -7200
# Node ID eaac6b2acd44ed8bd99a21f15c21ec0762d0ce94
# Parent  33f10a35ce20150c87a3cd9f2d4999bc58b576c7
8153267: nmethod's exception cache not multi-thread safe
Reviewed-by: aph, jcm

diff --git a/src/share/vm/code/nmethod.cpp b/src/share/vm/code/nmethod.cpp
--- a/src/share/vm/code/nmethod.cpp
+++ b/src/share/vm/code/nmethod.cpp
@@ -312,7 +312,8 @@
 
 
 address ExceptionCache::test_address(address addr) {
-  for (int i=0; i<count(); i++) {
+  int limit = count();
+  for (int i = 0; i < limit; i++) {
     if (pc_at(i) == addr) {
       return handler_at(i);
     }
@@ -328,7 +329,6 @@
   if (index < cache_size) {
     set_pc_at(index, addr);
     set_handler_at(index, handler);
-    OrderAccess::storestore();
     increment_count();
     return true;
   }
@@ -441,10 +441,11 @@
   assert(new_entry != NULL,"Must be non null");
   assert(new_entry->next() == NULL, "Must be null");
 
-  if (exception_cache() != NULL) {
-    new_entry->set_next(exception_cache());
+  ExceptionCache *ec = exception_cache();
+  if (ec != NULL) {
+    new_entry->set_next(ec);
   }
-  set_exception_cache(new_entry);
+  release_set_exception_cache(new_entry);
 }
 
 void nmethod::clean_exception_cache(BoolObjectClosure* is_alive) {
diff --git a/src/share/vm/code/nmethod.hpp b/src/share/vm/code/nmethod.hpp
--- a/src/share/vm/code/nmethod.hpp
+++ b/src/share/vm/code/nmethod.hpp
@@ -41,15 +41,16 @@
   Klass*   _exception_type;
   address  _pc[cache_size];
   address  _handler[cache_size];
-  int      _count;
+  volatile int _count;
   ExceptionCache* _next;
 
   address pc_at(int index)                     { assert(index >= 0 && index < count(),""); return _pc[index]; }
   void    set_pc_at(int index, address a)      { assert(index >= 0 && index < cache_size,""); _pc[index] = a; }
   address handler_at(int index)                { assert(index >= 0 && index < count(),""); return _handler[index]; }
   void    set_handler_at(int index, address a) { assert(index >= 0 && index < cache_size,""); _handler[index] = a; }
-  int     count()                              { return _count; }
-  void    increment_count()                    { _count++; }
+  int     count()                              { return OrderAccess::load_acquire(&_count); }
+  // increment_count is only called under lock, but there may be concurrent readers.
+  void    increment_count()                    { OrderAccess::release_store(&_count, _count + 1); }
 
  public:
 
@@ -241,7 +242,7 @@
   // counter is decreased (by 1) while sweeping.
   int _hotness_counter;
 
-  ExceptionCache *_exception_cache;
+  ExceptionCache * volatile _exception_cache;
   PcDescCache     _pc_desc_cache;
 
   // These are used for compiled synchronized native methods to
@@ -433,7 +434,7 @@
 
   // flag accessing and manipulation
   bool  is_in_use() const                         { return _state == in_use; }
-  bool  is_alive() const                          { return _state == in_use || _state == not_entrant; }
+  bool  is_alive() const                          { unsigned char s = _state; return s == in_use || s == not_entrant; }
   bool  is_not_entrant() const                    { return _state == not_entrant; }
   bool  is_zombie() const                         { return _state == zombie; }
   bool  is_unloaded() const                       { return _state == unloaded; }
@@ -576,8 +577,10 @@
   void  set_stack_traversal_mark(long l)          { _stack_traversal_mark = l; }
 
   // Exception cache support
+  // Note: _exception_cache may be read concurrently. We rely on memory_order_consume here.
   ExceptionCache* exception_cache() const         { return _exception_cache; }
   void set_exception_cache(ExceptionCache *ec)    { _exception_cache = ec; }
+  void release_set_exception_cache(ExceptionCache *ec) { OrderAccess::release_store_ptr(&_exception_cache, ec); }
   address handler_for_exception_and_pc(Handle exception, address pc);
   void add_handler_for_exception_and_pc(Handle exception, address pc, address handler);
   void clean_exception_cache(BoolObjectClosure* is_alive);
diff --git a/src/share/vm/runtime/vmStructs.cpp b/src/share/vm/runtime/vmStructs.cpp
--- a/src/share/vm/runtime/vmStructs.cpp
+++ b/src/share/vm/runtime/vmStructs.cpp
@@ -961,7 +961,7 @@
   nonstatic_field(nmethod,                     _stack_traversal_mark,                         long)                                  \
   nonstatic_field(nmethod,                     _compile_id,                                   int)                                   \
   nonstatic_field(nmethod,                     _comp_level,                                   int)                                   \
-  nonstatic_field(nmethod,                     _exception_cache,                              ExceptionCache*)                       \
+  volatile_nonstatic_field(nmethod,            _exception_cache,                              ExceptionCache*)                       \
                                                                                                                                      \
   unchecked_c2_static_field(Deoptimization,    _trap_reason_name,                             void*)                                 \
                                                                                                                                      \